(1) This invention relates to display devices and more particularly to display devices which employ gas panels.
(2) Earlier types of gas panel display devices employed rather complex circuit arrangements for driving the numerous horizontal and vertical coordinate drive lines. Since high voltages were involved, this required high voltage components, and in many cases a separate transformer and high voltage transistors were employed for each one of the vertical drive lines and each one of the horizontal drive lines. Integrated circuitry could not be employed because of the high voltage requirements. Consequently, the use of the more expensive transistors and transformers resulted in increased cost of manufacture and maintenance. Even then, moreover, there was a lack of uniformity in the magnitude of the drive signal over the entire panel.
The drive signals for the horizontal lines and vertical lines of gas panel devices must be uniform within a relatively high degree of precision and the dynamic characteristics of every cell must be uniform within a relatively high degree of precision if reliable writing and erasing operations are to take place selectively. As the number of cells per unit area on the panel increases, the need for still greater precision is required of the drive signals applied to the horizontal and vertical coordinate drive lines. The presence of half-select write and erase signals on non selected cells increase the problem as the density of cells on the gas panel increases. The half-select signals are signals applied to all gas cells on the selected horizontal line and the selected vertical line. The potential difference applied across the selected gas cell for a write operation exceeds the ignition potential of this cell. The violent plasma discharge activity in the selected gas cell tends to "spill" over to adjacent cells, and this raises the undesirable prospect of possibly igniting adjacent cells, particularly those receiving a half-select potential difference. When the write pulse of a selected gas cell is coincident in time with the sustain avalanche of adjacent cells, the violent plasma discharge activity taking place in the gas can and does change the turn-on and turn-off characteristics of affected gas cells nearby. Moreover, the number of sustaining cells adjacent to each given dark cell and their proximity is an ever changing combination of variables resulting in different cell histories and character fonts. This makes the turn-on characteristic of any given cell unpredictably variable, and it tends to make selective write and erase operations virtually impossible. One solution is to mechanically isolate cells so that plasma discharge activity in one cell does not "spill" over to adjacent cells. However, this poses many technical and economic problems if resort is made to the mechanical isolation of each cell by the so called "honeycomb" construction. Even the use of honeycomb construction does not provide electrical isolation, and the problem of half-select signals is nevertheless present on various non selected gas cells.